1. Field of the Invention
The present invention relates to a control technology and method of an engine equipped with an exhaust gas recirculation (hereinafter referred to as “EGR”) apparatus that returns part of exhaust gas to an intake pipe.
2. Description of the Related Art
In the field of diesel engines, and the like, there is known a technology for concurrently reducing soot and NOx by using the effect of reducing the combustion temperature based on the application of the exhaust gas recirculation (EGR), and the effect of uniformalizing a mixture gas by increasing an ignition delay period. The combustion temperature and the ignition delay period are influenced by the in-pipe inert gas (CO2) concentration and the in-cylinder oxygen concentration that change by the introduction of EGR. Therefore, in order to carry out the engine control, it is important to correctly detect/estimate not only the EGR rate but also the inert gas concentration or the in-cylinder oxygen concentration. For example, as an estimation method for estimating the in-cylinder oxygen concentration, JP-A-2003-27997 discloses a technology for determining the control amount relating to fuel injection. According to this technology, the control amount is determined by detecting the exhaust gas oxygen concentration by an O2 sensor, and then by estimating the in-cylinder oxygen concentration by use of the exhaust gas oxygen concentration.